DVB-S2 is the second generation satellite broadcasting standard for transmitting video and data over satellite. This standard supports backward compatibility modes to DVB-S standards as well as supporting several new developments in channel coding. This improved standard supports both preconfigured constant transmission rate transmission, known as CCM, and variable and adaptive transmission modes (VCM and ACM) that support modulation and coding rate changes. The improved standard uses a train of frames where each frame can have different Modulation and Coding rates (also known as MODCODs). The frame of data packed per DVB-S2 standard, is called a BBFrame. Data packets, such as MPEGs, are placed in the BBFrame, while the BBFrame's header supplies information that enables the dis-assembly of the Data Packets at the reception. The BBFrames has variable length, spanning from 3072 to 58192 bits, depending on the code rate and on the code selected block length (two options for code block length exists, either 16200 or 64800 coded-bits long). The BBFrames are further processed by Modulator, providing error correction encoding, adding headers and finally RF-modulating “PLFrames”, referred to simply as Frames. DVB-S2 efficiency depends on the algorithm used for packing user packets, such as MPEGs, into the BBFrames, and on the algorithm of the transmission order of the Frames.
Another important issue is how to control the data sources transmit rate, so that the data sources provides a data rate that is not larger, on the average, than the actual transmission average data rate, and on the other hand, the maximal data rate capacity of the transmission can be utilized. Note that this mission is complex, because the data rate at ACM mode is not constant.